Unreinforced masonry building (general)

An overview of potential strengthening solutions for unreinforced masonry buildings.

To find solutions that are appropriate for your building, consult a structural engineer for a professional assessment.

Unreinforced masonry building image
Image courtesy of Gavin McLean

Hazard

Parts of the building or entire building collapses.

Potential structural strengthening projects

Fit and fix plywood shear-walls up through the building

Fit and fix existing or new timber wall framing between the existing flooring and floor framing of the floor above. Fit and fix plywood sheets to one or both sides of the wall framing to form a ‘shear wall’. You may need hold-down ties at each end of the shear-wall to resist overturning of the shear-wall in its own plane. The hold-down may be fitted up the full height of the wall and fixed down into the foundations of the shear-wall.

Form or strengthen a floor or roof structure (diaphragm)

  1. Overlay existing flooring with plywood to form a structure (diaphragm):
    Overlay existing flooring with plywood. Screw it down to the existing flooring and floor framing. To provide adequate load transfer between sheets of plywood, lay a light-gauge galvanized steel strip under the plywood joint with the centerline of the steel strip on the joint line. The screws on the perimeter of each plywood sheet will pass down through the plywood and steel strip, into the flooring and floor framing.
  2. Make the floor structure (diaphragm) continuous by fixing through bottom plate of partitions:
    Where the plywood of the floor structure (diaphragm) abuts a wall, fold a light-gauge galvanized steel angle and fit it into the angle formed by the floor and the wall. The plywood sheet perimeter edge-fixing screws pass down through the plywood and the horizontal leg of the angle, and into the flooring below. Before fitting the wall linings, fix the vertical leg of the angle into the wall’s bottom plate with screws.
  3. Where the supporting shear wall in the space below is not aligned with a wall in the floor above, fit and fix new timber framing (blocking) between the top plate of the wall below and the flooring on which the plywood structure (diaphragm) is fitted. Place a light-gauge galvanized steel strip under the plywood, over the centre line of the wall top plate below. Screw the plywood down through the steel strip and the flooring, into the blocking below.
  4. Fit flat-strap bracing in ceiling space to make structure (diaphragm):
    To provide enhanced bracing capacity within the restricted space under a pitched-roof structure, install proprietary galvanized steel strips. Depending on the capacity required, screw multiple strips to timber framing (blocking) that is pre-fitted and fixed into the roof or ceiling framing. The steel strip bracing is provided pre-punched for the screws, and packaged into a coil pack for easy of delivery into the roof space.

Fix masonry facade or wall to floor or roof structure (diaphragm)

Tie the masonry back onto supporting floor and roof structures (diaphragms). Grout steel dowels into the brickwork and fix them to blocking fitted between the joist members. In turn, fix the blocking to the adjacent joists. Provide plywood perimeter strips and additional nailing down into the joist to carry the face loading from the masonry wall into the structure (diaphragm) so that the seismic inertia load can be transferred to walls parallel to the loading.

Possible first steps with a structural engineer

They assess the structural capacity of the masonry building and provide specifications for the required strengthening work.